[Free-radicals formation in reductions of flavin. Study on the reduction of aminoethylcellulose-bound flavin].

The reduction of flavin by reduced diphosphopyridine nucleotide and photoreduction were studied spectrophotometrically. Flavin was covalently bound to aminoethylcellulose, therefore the interaction between flavin molecules was excluded. Nevertheless a considerable quantity of free radicals was demonstrated under these conditions. The experimental dependence of the radical concentration as a function of reduction degree is readily explained if the reduction of flavin proceeds in two consecutive one-electron steps. The ratio of the rate constants of both reactions for the reduction of flavin by NADH k2'/k1' was equal to 4, for the photoreductions k2'/k1' to 6.5.